This is the Du-Bro RC Heavy Duty Adjustable Control Horn for .40 - .91 size airplanes. These Heavy Duty adjustable control horns are the latest in a family of innovative control horn applications. The self-adjusting horn will mount straight (90º to center line of control surface) against the angled control surface using no wedges or shims! With two sizes available, your aircraft will be even more functional as well as stylish.